In recent years, there have been rapid expansions of the fields of digital computers and robotics in the consumer markets. The proliferation of such devices has resulted in an increased need for means for communicating digital data between multiple devices. For instance, digital computers require input and output devices from which and to which digital data is transferred. Robots, which perform complex acts which emulate certain human functions, are typically controlled by a remote computer or receive program information from a remote computer.
In any case, the transfer of digital information between devices is generally accomplished by connecting devices with one or more electrically conducting wires. This requirement that the devices be electrically connected significantly reduces the portability or transportability of the devices, since the data communications wiring must remain connected. For instance, although a computer may be constructed which is portable, generally a printer is not readily relocatable. Thus, although the computer could be moved from room-to-room, such moves would be limited by the ability to maintain the wired interconnection between the computer and the printer.
Although means are available for interconnecting remote devices, such as using a modem with a standard telephone system, such means are not practical when the remote devices are located within the same general area. Furthermore, devices connected by modems are not truly portable since they must be electrically connected to the telephone network.
One possible solution to obtaining data communications between devices without requiring the devices to be electrically connected is the use of radio communications. However, one cannot simply interconnect two digital devices with a radio transmitter and receiver and initiate communications between the devices. Radio frequency communications within the United States are heavily regulated and restricted as to use. Very few channel frequencies are available for the type of communication described above. Furthermore, those frequencies which are available are restricted to a limited number of licensed users. The burden and expense of obtaining a license and equipment to operate on a typical frequency band allocated to digital data communications makes such operation impractical for the casual user.
The Federal Communications Commission has recently made a new frequency band available for low power communications. A low power communication device may be operated on one or more of the frequencies 49.830 MHz, 49.845 MHz, 49.860 MHz, 49.875 MHz or 49.890 MHz, without any restriction on the type of modulation; however, the device is restricted to a self-contained unit according to 47 C.F.R. .sctn. 15.117-15.119. In other words, the device cannot be electrically connected to an external device, such as a computer. The principal reason behind this particular rule is apparently to avoid any spurious radio transmissions which might occur on any electrical wires connected to the transmitting device. Furthermore, the limitation prevents a user from placing the transmitter at a high elevation and connecting it to a remote data source, thus, increasing the communications range. Typical utilization of the frequencies are for remote control toys and for cordless telephones.
The typical range of such a transmitting device of approximately 300-700 feet is well-suited to communications between digital devices in a typical office or residential area. The frequencies listed would be ideal for transmitting digital data communications between a computer and a peripheral device or between a computer and a mobile robot; however, the restriction of no electrical connection between the transmitting unit and another device makes such frequencies unavailable using conventional interconnection means.
As set forth above, a need exists for a device which allows communications between digital devices on the unlicensed frequency range of 49.82 to 49.90 MHz. However, since electrical interconnections are prohibited by Federal Communication Commission's regulations, such need cannot be fulfilled by ordinary interconnection means.